Abstract

Ammonia falling film and pool boiling evaporation experiments were conducted on three horizontally placed types of stainless tubes, namely smooth, low fin and 3D fin and enhancement of heat transfer was examined. For the falling film tests, heat transfer coefficients of the smooth tube decreased with increasing circumferential angle starting from the top of the tube. For finned tubes, however, liquid film was held between the fins, thus causing decrease in heat transfer coefficients. A comparison of average heat transfer coefficients in the low Reynolds number range shows that the smooth tube had the highest heat transfer coefficients followed by 3D and low finned tubes respectively. Heat transfer enhancement by the fins was not observed. In the high Reynolds number range, convection occurred in the liquid film between the fins of the 3D tube but it was not very significant and the heat transfer coefficients are similar to those of the smooth tube. Pool boiling heat transfer coefficients of the smooth tube agree well with Jung et al. correlation while those of the low fin and 3-D fin are 20-30% lower. A comparison of falling film and pool boiling heat transfer coefficients of the three types of test tubes shows that falling film heat transfer is higher than pool boiling.